Method for determining the concentration of a metal in an alloy melt

ABSTRACT

The method for the direct quantitative measurement of a metal in a molten metal mixture or alloy using a galvanic cell is described.

United States Patent Wilder Assignee: Kennecott Copper Corporation,

New York, NY.

Filed: Mar. 28, 1972 Appl. No.: 238,937

Related US. Application Data Continuation-impart of Ser. No. 31,425,April 14, 1970, abandoned, which is a continuation-in-part of Ser. No.704,863, Feb. 12, 1968, abandoned.

us. Cl. 204/1 T, 204/195 5 Int. Cl. 00111 27/46 Field of Search 204/1 T,195 S; 324/29; 23/230 R Inventor:

References Cited UNITED STATES PATENTS l/1967 Alcock .l 204/195 STHERMOCOUPLE LEADS June 11, 1974 12/1969 Kolodney et a1. 204/195 S OTHERPUBLICATIONS Fitterer, Journal of Metals Reprint, pp. l-6,

Vol. 2

39, pp. l,276-l,281 Sept. 1967.

1 Primary Examiner-G. L. Kaplan Attorney, Agent, or FirmLowell H. McCarter; John L. Sniado ABSTRACT The method for the direct quantitativemeasurement of a metal in a molten metal mixture or alloy using agalvanic cell is described.

5 Claims, 2 Drawing Figures ELECTRICAL CONDUCTORS TO POTENTIOMETERREFRACTORY PLUG ELECTRICAL CONDUCTORS 7 IN REFRACTORY SHEATH ELECTROLYTETUBE 1 REFRACTORY CEMENT 1 1 4 Z THERMOCOUPLE IN QUARTZ WELL v 2 2 g s 2DISC CONTACT 5 4 ,1; El /fl "fa/5i Z1 REFERENCE ELECTRODE MOLTEN METALBATH PATENTEBJIIII I I IIII I 3.816269 THERMOCOUPLE LEADS ELECTRICALCONDUCTORS 7\ -F 7T0 POTENTIOMETER REFRACTORY CEMENT L REFRACTORY PLUG i2 Z s I THERMOCOUPLE fi ELECTRICAL CONDUCTORS IN QUARTZ WELL 3 INREFRACTORY SHEATH 2 2 j ELECTROLYTE TUBE DISC CONTACT\ I;

::': k :EE ZT; I :Iu

M T M A A REFERENCE ELECTRODE 0L EN ET L B TH FIGURE I CELL FORMEASURING METAL CONCENTRATION IN MOLTEN BATH INVENTOR:

Thomas C. Wilder 305-- I 22 24 26 28 3O 32 34 BY- WT. ZINC L mfg 13 2H|$ ATTORNEY EMF OF CELL VS ZINC CONCENTRATION IN MOLTEN BRASS METHODFOR DETERMINING THE CONCENTRATION OF A METAL IN AN ALLOY MELT Thisapplication is a continuation-in-part of application Ser. No. 31,425filed on Apr. 14, 1970 now abandoned which in turn is acontinuation-in-part of application Ser. No. 704,863 filed on Feb. 12,1968 now abandoned.

This invention relates to an electrochemical cell for the determinationof the concentration of a metal .in molten metal alloy or a mixture ofmolten metals. The method of this invention is an important tool to thepro cess metallurgist in the preparation of alloys.

Prior to applicants invention it was not possible to directly determinethe concentration of a metal in a molten metal bath. Prior methodsrequired substantial amounts of time to make a quantitativedetermination of the metal composition. Chemical methods for determiningmetal concentration in alloys require up to about 30 or more minutes.Spectrographic analysis requires less time but again is not of any realsignificance to a process metallurgist while a melt is in process.

It is therefore an advantage of this invention that the apparatus andprocess claimed herein can be used to advantage by a processmetallurgist in the working of a molten bath of metal alloys. Theprocess metallurgist may make a determination substantiallyinstantaneous and make the necessary adjustments to the molten bath tobring the metal compositions into the specification range required. Thisinvention will eliminate the errors in adjusting the chemical analysisof a molten metal bath.

It is well known that in the working ofa molten metal bath that the mostvolatile component thereof may leave the bath during the processing.Thus by the time that a wet method chemical analysis or a spectrographicchemical analysishas been performed the composition of the molten metalbath may have changed sufficiently so that the analysis is no longeraccurate. The method of this invention gives a quantitativedetermination for the most chemically reactive metal in a' molten metalbath so that the composition of the bath may be adjusted by the additionof a metal or alloy to the desired composition just prior to casting.

It is known, for example, that the oxygen content of liquid metals maybe determined using a galvanic cell; see U.S. Pat. No. 3,481,855, M.Kolodney et al; U.S. Pat. No. 3,359,188, W. A. Fischer and U.S. Pat. No.3,297,551, C. B. Alcock. In these patents the oxygen content must bebelow the concentration where the oxygen forms an oxide with the solventmetal. Thus if the oxygen content is at the saturation point the EMF isat its minimum reading. Thus the Fischer and Alcock apparatus andmethods have limited application.

The literature also contains many references to methods and systems formeasuring oxygen content of liquid metals. See, for example, Wilder, T.C., Transactions of the Metallurgical Society of AIME, Vol. 236, July1966, pp. 1035-1040; Fritterer, G. R., Journal of Metals, Reprint, Aug.1966, pp. 1-6; Wilder, T. C., Transactions of the Metallurgical Societyof AIME, Vol. 236, Jan. 1966, pp. 88-94; and Schwerdtfeger, K.,Transactions of the Metallurgical Society of AIME, Vol. 239, Sept. 1967,pp. 12764281. The articles all discuss use of galvanic cells formeasuring the thermodynamic properties of liquid metal alloys or theoxygen content of metals and alloys. However neither the technicalliterature nor the patent literature suggest that the concentration ofthe most chemically reactive metal in a molten alloy can be determinedusing a galvanic cell. Applicant has, therefore, devised a novel methodfor measuring the concentration of a metal in a molten alloy using agalvanic cell.

According to the present invention, the concentration of the mostchemically reactive metal in a melt of a metal alloy is measured by amethod which comprises preparing calibration curves by l) measuring theelectromotive force across a galvanic cell inserted into a molten metalalloy wherein one electrode comprises the molten metal alloy, the otherelectrode is a refer ence electrode comprising a mixture of a metal andits oxide or a gas of known oxygen potential at the same temperature asthe molten alloy, and the electrolyte is a solid anionic conductor, (2)chemically analyzing samples of the alloy to determine the concentrationof the most reactive metal, (3) plotting calibration curves of themeasured electromotive force across the cell corresponding to theanalyzed concentration of the most reactive metal in the molten alloy,and (4) determining from such curves and a measured electromotive forcethe concentration of the most chemically reactive metal in a melt of themetal alloy.

The most reactive metal, whose concentration is to be measured, in amelt of an alloy is defined as the metal which has an oxide which has anoxygen potential less than that of the oxygen normally dissolved in thesolvent metal. The process of this invention applies to any alloy systemin which this fact is observed. 1 have specifically found that my methodis applicable to the following alloy systems: nickel concentration canbe measured in molten copper-nickel alloys, aluminum concentration canbe measured in molten aluminumbronzes, zinc concentration can bemeasured in molten brasses and chromium concentration can be measured inmolten stainless steels. Thus more specifically the invention herein isa method of measuring the concentration of a metal in a melt of analloy, said metal having an oxide which has an oxygen potential lessthan that of the oxygen normally dissolved in the solvent metal of amolten alloy, said molten alloy selected from the group consisting ofcopper-nickel alloys, aluminumbronzes, brasses, and stainless steels,which method comprises 1) determining which metal in the alloy has anoxide which has an oxygen potential less than that of the oxygennormally dissolved in the solvent metal of the molten alloy, (2)measuring the electromotive force across a galvanic cell inserted intothe molten alloy, wherein one electrode comprises the molten alloy, theother electrode is a reference electrode comprising a mixture of a metaland its oxide at the same temperature as the molten alloy and theelectrolyte is a solid anionic conductor, (3) plotting calibrationcurves of the measured electromotive force across the cell to correspondto the concentration of the metal having an oxide which has an oxygenpotential less than that of the oxygen normally dissolved in the solventmetal of the molten alloy, and (4) determining from such curves theconcentration of the metal in the melt of the alloy.

Determining the metal in an alloy that has an oxide which has an oxygenpotential less than that of the oxygen normally dissolved in the solventmetal can be accomplished by measuring, analyzing or calculating. Thesethree methods are discussed below.

The chemical potential of oxygen in molten copper may be measured by acell consisting of a solid oxide electrolyte (such as stabilizedzirconia), one electrode of known oxygen potential (such as air, pureoxygen, or a mixture of a metal and its oxide), and the other electrodecopper containing dissolved oxygen but no other dissolved material.Another method is to pass a gas mixture of known oxygen potential, suchas a mixture of CO and CO over molten pure copper for several hours,quench the copper and then analyze for the oxygen content correspondingto that oxygen potential.

The chemical potential of oxygen in oxides may also be calculated fromthe known free energy of formation of the oxides. The free energy offormation of the oxides are tabulated in many reference sources as afunction of temperature. If the free energy of formation of an oxide isunknown it may be determined in the laboratory using a cell consistingof a solid oxide electrolyte, one electrode of known oxygen potential,and the other electrode a mixture of the oxide with its metal. Anothermethod utilizes the measurement of the concentration ratios of anoxidizing and reducing gas, such as H and H which are in equilibriumwith an oxide. At equilibrium the oxygen potential of the gas will alsobe the oxygen potential of the oxide.

A calculation of the type described above follows. This calculationshows that the oxygen potential in zinc oxide is less than that ofoxygen normally dissolved in molten copper, so that a cell, such asdescribed herein, when immersed in a molten copper-zinc alloy (i.e.,brass) will measure the zinc content of the alloy (i.e., the zinc-zincoxide equilibrium in molten copper-zinc alloy) and not the overalloxygen content of the alloy.

At 1,200 C the chemical potential of oxygen dissolved in molten copper,a (in Cu) has been measured in the laboratory (T. C. Wilder, Trans. Met.Soc. AIME 236, 1966, pp. lO35l040), and is equal to 0.205 times theoxygen concentration expressed as a mole fraction, X hence:

a (in Cu) 0.205 X If the oxygen normally dissolved in copper such asmolten cathode copper is parts per million by weight, or 0.001 weightpercent then a (0.205) (0.001 )/l00 X 63.54/l6 8.1 X 10 where 63.54 isthe atomic weight of copper and 16 the atomic weight of oxygen. Now thefree energy of formation of zinc oxide at l,200 C is 45,860 cal/gfw(C.E. Wicks and F. E. Block, U.S. Bureau of Mines Bulletin No. 605, p. 138)or,

k O (g) Zn(g) ZnO (s) AF",= 45,860 cal.

ide, it first must be assumed that the oxide is in equilibrium with purezinc vapor and thus p 1. Thus:

45,860 RTln (1./p0 6' 45,860 /2 RTln p 0 1 0 :22 1? 10 which is lowerthan the chemical potential of oxygen normally dissolved in copper atthe same temperature. Thus it is clear that the oxygen potential of zincoxide (2.47 X 10) is lower than the oxygen potential of the oxygennormally dissolved in cathode copper (8.1 X 10'). Any new oxygen such aspick-up from air, absorbed by a copper-zinc alloy will, in effect, reactwith zinc to form ZnO. A cell such as that described herein will show achange in the measured electromotive force caused by the removal of thesoluble zinc from the copper-zinc alloy.

The galvanic cell used in measuring the electromotive force may, ingeneral, be represented by The electromotive force (EMF) of this cell issubstantially a simple function of the concentration of the metal to bemeasured. Thus the potentiometer may be calibrated to give a directreading of the concentration of the metal in the alloy.

The galvanic or electrochemical cell that can be used for themeasurement of the concentration of a metal in an alloy comprises asolid electrolyte and a reference electrode enclosed in the electrolyte.The reference electrode in the solid electrolyte is electricallyconnected to a potentiometer. An electrical conductor has one endattached to a potentiometer and the other end of the conductor isadapted to be in contact with the liquid metal alloy whose specificmetallic concentration is to be measured. The cell is calibrated bydetermining the electromotive force (EMF) with a given electrode andmetal by comparison with chemical analysis of the alloy containing themetal whose concentration is being measured. This data is convenientlycorrelated in a table or family of curves with parameters of metalconcentration and electromotive force (EMF).

The cell and process of this invention can be used for measuring theconcentration of the most active metal in the alloy compositionsprovided that the oxygen potential of the metals oxide is less than theactivity of the oxygen normally dissolved in the solvent metal. In otherwords, the invention embraces the measurement of the most chemicallyreactive metal in a molten alloy providing enough oxygen is present tocause the formation of small amounts of that metals oxide. Specificexamples of metal concentrations that can be measured in moltenengineering alloys include nickel in coppernickel alloys, aluminum inaluminum-bronzes, chromium in stainless steels and zinc in brasses.These alloys are given as specific examples but are not to be consideredas limiting the scope of this invention except as defined in theappended claims.

The applicant has discovered that the chemical thermodynamic activity ofthe most active metal in a molten alloy makes it possible to determinethe concentration of the most chemically reactive metal in the alloy bymeasuring the EMF across a galvanic cell and calibrating it so that themeasured EMF corresponds to the metal concentration. The residual oxygenin the molten alloy forms an oxide with the most chemically reactivemetal. In the case of brass, as determined by available thermodynamicdata, the residual oxygen must be substantially less than 1 part permillion, i.e., about 0.005 ppm, before a separate phase of zinc oxidewill not form.

The theory of the invention will be explained as applied to the brasssystem where a nickel-nickel oxide reference electrode is used. Howeverit is to be understood that this theory is presented by way ofexplanation. It is not considered to be limiting except as defined inthe appended claims. In the brass system the zinc forms a zinc oxidephase with whatever residual oxygen may be in the metal. Since zincoxide forms in the Cu-Zn-O system with less than one ppm oxygen in themolten alloy the EMF measurement is not measuring the oxygen content ofthe molten metal.

By way of further explanation of how this cell functions, the reactionwhich occurs when the circuit of the cell is closed is:

free energies of formation of ZnO and NiO respectively, R is theuniversal gas constant, T is the absolute temperature in degrees Kelvin,and a is the thermodynamic activity of zinc in the molten copper-zincalloy. At constant temperature, all the terms in equation 2 are constantexcept 6 and az The latter term is directly related to the concentrationof zinc in the alloy; hence the value of e is directly related to theconcentration of zinc in the alloy.

The reason that 55;? (BT36 (Z716) ausrsti'si'ih the brass is explainedas follows. The standard molar free energy of formation of ZnO, and themolar free energy of oxygen in ZnO at 995 C is about 5 1,500 cal/mole.The molar free energy of oxygen in solution with copper at 995 C isabout -6390 5825 log X where X is the mole fraction of oxygen in copper.At the point where the molar free energy of oxygen in copper isequal tothat in ZnO (obtained by equating l,500 and 6390 5825 log X X is 1.8 XlO which converts to 0.005 parts per million of oxygen. At anyconcentration of oxygen in molten brass in excess of this infinitesimalamount, ZnO must exist as a separate discreet phase in the system,and'the only reaction which can occur is the one shown in equation 1. Asubstantially similar calculation may be made to show that a vanishinglysmall amount, i.e., less than about 1 ppm, of oxygen is required to formA1 0 from molten aluminum bronzes, or Cr O from molten stainless steels.

The ability to measure the concentration of a metal in a molten alloy asdescribed arises from the phenomenon that most of the oxygen in thealloy systems is in the form of a solid metal oxide, i.e., MeO(s) (whereMe is the metal whose concentration is to be measured) and that theelectromotive force of the cell is a function of the Me-MeO (metalmetaloxide) equilibrium wherein the metal, Me is not at unit activity butdissolved in the alloy. Therefore the process can be used to measure themetal concentration in any alloy system in which the most active metalforms a separate oxide phase before the overall oxygen content is largerthan would be desired in the alloy.

Using the method of analysis as described above with reference to thecopper-zinc system, the applicant has determined that nickel is the mostchemically reactive metal in copper-nickel molten alloys, aluminum isthe most chemically reactive in aluminum-bronzes molten alloys (maycontain in addition to copper and aluminum such elements as iron, nickeland manganese), and

chromium is the most chemically reactive in stainless steels.

Having determined, by one of the three methods discussed above, the mostchemically reactive metal in the molten alloy bath at the melttemperature the next step is to prepare calibration curves. FIG. 2contains calibration curves at two melt temperatures for determining theconcentration of zinc in molten brass. A series of electromotive forcereadings was taken and a sample of the alloy for chemical analysis waswithdrawn from the melt. The composition of the melt was then changedeither by allowing the most volatile metal component to vaporize fromthe melt, as zinc in the molten brass, or by adding weighed amounts of apure metallic component to the melt. Then another series ofelectromotive force readings was taken and another sample of the alloywas withdrawn from the melt. These steps were repeated until asufficient number of electromotive force readings and alloy samplechemical analyses have been made to give data for preparing thecalibration curves. It is particularly advantageous to preparecalibration curves for each alloy at a number of different temperatures.interpolations can then be made when the melt temperature does notcorrespond to one of the calibration curves.

Any of a number of different electrolytes may be used within the scopeof this invention. However the electrolyte must be characterized asbeing primarily an anionic conductor. The electrolytes are those thatallow the movement of oxide ion vacancies under the influence of anoxygen potential gradient. The electrolyte must not be porous to theextent that a metal or its alloy penetrate the electrolyte to the degreethat would cause a short circuit.

Any electrolyte ifiat'i'riets the arsreaaemisnathap acteristics may beused within the scope of this invention. The electrolyte generallyconsists of a host material and a dopant material to a minor extent,i.e., from about 5 to 25 percent dopant. The dopant dissolves in thehost material causing the host material to have a number of anionicvacancies. This results in an electrolyte as being primarily an anionicconductor. The electrical conduction is by the movement of oxide ionvacancies. Suitable electrolyte host materials include the oxides ofthorium and zirconium, to which an oxide of the alkaline earths or rareearths, e.g., calcium oxide or yttria have been added to form a solidsolution. The host material, e.g., thoria or zirconia, and the dopant,e.g., calcium oxide, are mixed in the desired proportions and cast intothe shape of the desired electrolyte, for example a closed-end tube orcrucible. The preferred electrolyte is a calcia stabilized zirconiacontaining about 92.5 percent zirconia and about 7% percent.

calcium oxide. This calcia stabilized zirconia is commercially availableunder the trade name of ZlR- COA."

Enclosed in the electrolyte is a reference electrode material. A gas ormixture of gases of known oxygen potential may be used as the referenceelectrode. The preferred gas is oxygen. Suggested mixtures of gasesinclude air, carbon monoxide and carbon dioxide, and hydrogen and watervapor. However the preferred reference electrode is a metal in admixturewith its oxide. Specific examples of these reference-electrodes includea mixture of iron and iron oxide, chromium and chromium oxide, copperand copper oxide, nickel and nickel oxide, titanium and titanium oxideand molybdenum and molybdenum oxide. Any mixture of a metal and itsoxide that is a solid at the melt temperatures and has relatively stablethermodynamic properties may be used as the reference electrode.Generally the reference electrode will contain about equal portions ofthe metal and the metal oxide.

The reference electrode may be prepared by mixing equal volumes ofscreened and sized metal and metal.

oxide powders. The powders are thoroughly blended in a rotary mixer orthe like. The mixed metal and metal oxide powders are compressed andsintered in the electrolyte tube. Contact to the metal/metal oxidesintered pellet may bemade by a platinum disc spot welded to a platinumwire or other electrical conductor. The platinum wire or electricalconductor may be sheathed in a protective tube of quartz, alumina or thelike so that mechanical pressure may be applied to the platinum disc.

Contact to the molten metal bath is made with an electrical conductorsheathed in aquartz, alumina, or the like, protective tube. The moltenmetal bath contact electrical conductor is selected so that it is notdissolved or corroded by the molten metal bath.

Because of the relative sensitivity of the measurements required in thisinvention it is preferred to use platinum leads from the referenceelectrode in the electrolyte to the potentiometer and an electricalconductor from the molten bath to the potentiometer selected so that itis not attacked by the molten metal bath. Specific examples ofelectrical conductors from a brass melt to the potentiometer aretantalum, tungsten, rhenium, molybdenum and the alloys thereof.

The reproducibility of the cell potential for most alloy systems isexcellent. It is also very sensitive to slight composition changes.Owing partly to the low electrical resistivity of the electrolyte, cellpotential.

may be resolved to the nearest 0.1 millivolt. This means thatacomposition change of 0.02 weight percent can be detected if thetemperature is accurately known. Thus if the temperature in the area ofthe melt containing the cell is known to i 2 C. the metal concentrationcan be determined with a range narrow enough to meet most requirementsof the process metallurgist. I

FIG. 1 shows pictorially a preferred embodiment of the electrochemicalcell of this invention in a molten metal bath.

FIG. 2 graphically presents the electromotive force of a cell as afunction of zinc concentration in moltenbrass.

EXAMPLE 1 This example illustrates an electrochemical cell in accordancewith this invention as it is used to directly measure the zinc contentof molten copper-zinc alloys.

'el/nickel oxide pellet was made by a platinum disc spot welded to aplatinum wire. The platinum wire was sheathed in a quartz tube so thatmechanical pressure could be applied to the platinum disc. Contact tothe molten copper-zinc bath was made by a tantalum wire sheathed inalumina. A tantalum contact was chosen since it does not dissolve in themolten copper-zinc alloy.

A Alumina aemama useata eai'arrtii'iinrior of I the electrolyte bodyfrom condensing zinc vapor con- Pt Ni, NiO 'zro 2 7 /2%CaO Zn(inCu), ZnOTa tamination. A thermocouple in a quartz well was provided to giveaccurate temperature measurements in the region of the electrolyte andthe molten copperzinc alloy contact.

This electrochemical cell maybe representedas V POTENTIOMETER i Theinternal cell similar to that shown in FlG. l was placed in an aluminacrucible adapted to be heated in .a resistance furnace. The brass (249grams, 30 percent' zinc) whose zinc concentration was to be measured wascharged to the crucible and melted. The composition of the alloy waschanged by either allowing the zinc to vaporize from the melt, or byadding weighed amounts of pure copper. The zinc oxide present in thecopperzinc melt, as shown in the cell above resulted from the reactionof zinc with trace amounts of oxygen present in the atmosphere above themelt. in all cases samples were taken correspondingly to each readingand a chemical analysis was made. Readings were taken for various alloycompositions at 995 C and 1,069 C.

Cell potentials were measured with a null potentiometer. The dataobtained are shown in the Table and plotted with the parameters of zincconcentration and EMF as shown in FIG. 2.

Thr'fiFodFcfiiit f the cell potential was'excellent and was verysensitive to slight composition changes. Cell potentials were easilyresolved to the nearest 0.1 mV. This meant that a composition change of0.02 weight percent zinc could be detected if the temperature isaccurately known. Thus if the temperature in the area of the meltcontaining the electrochemical cell is known to i 2 C then themeltscomposition can be determined to i 0.06 weight percent zinc.

TABLE Potentials of Cell as Function of Zinc Concentration in MoltenBrass at 995 C Alloy No. Wt. Pct. Zn EMF of Cell, mV

at 1069 C EXAMPLE 2 Wtsfct. Zn EMF of Cell, mV

Alloy No.

B. A copper-zinc alloy containing from about 5.5% to about 13.0% of zincwas held at 1,069 C. The EMF readings, in millivolts, across theelectrochemical cell are tabulated below.

Alloy No. Wt. Pct. Zn EMF of Cell, mV

LII

The nickel concentration in a copper-nickel alloy melt may be measuredusing a nickel/nickel oxide reference electrode in a zirconiumoxide-calcium oxide electrolyte. Where the system has a low chemicalpotential it is preferable to use an electrolyte of doped thorium oxide.

Where a system using a particular reference electrode develops largeelectromotive forces thus giving rise to possible electrode polarizationit is preferable to use a reference electrode other than nickel/nickeloxide. Thus in measuring the aluminum concentration in aluminum-bronzemelts it is preferred to use a chromium/chromic oxide referenceelectrode in a thorium oxide electrolyte doped with calcium oxide ormagnesium oxide. Chromium concentration in stainless steel melts ismeasured using the chromium/chromic oxide reference electrode.

In one embodiment of this invention it is contemplated that theelectrochemical or galvanic cell may be adapted to be inserted directlyinto the melting vessel containing the molten metal.

In another embodiment within the scope of this invention the galvaniccell is suspended in a vessel such as an alumina crucible. The crucibleand cell are placed in a small furnace conveniently located near themelt ing pot. The furnace is maintained at a temperature complimentingthat of the molten metal alloy in the melting pot. In operation, amolten metal sample is re moved in any convenient manner from themelting pot and transferred immediately to the crucible in the furnace.The EMF of the galvanic cell is then measured on a potentiometer todetermine the concentration of a metal in the molten metal.

What 1 claim is:

1. A method of determining the concentration of zinc in molten brasscontaining at least 0.005 parts per million oxygen which comprises:

a. preparing a bath of molten brass,

b. taking samples of said molten brass at time intervals while addingzinc to said molten brass,

c. measuring the electromotive force across a galvanic cell insertedinto said molten brass simultaneously with the taking of each sample,wherein one electrode comprises said molten brass, the other electrodeis a reference electrode comprising a mixture of a metal and its oxideor a gas of known oxygenpotential at the same temperature as said moltenbrass and the electrolyte is a solid anionic conductor,

d. analyzing each sample for zinc,

e. plotting calibration curves of zinc versus electromotive force basedon electromotive force measurements from step (c) and zinc analyses fromstep (d), and

f. in a second bath of molten brass containing at least 0.005 parts permillion oxygen, measuring in said second bath the electromotive force asin step (c) and obtaining from the calibration curve plotted in step (e)the concentration of zinc in said second bath of molten brass.

2. A method of determining the concentration of nickel in moltencopper-nickel alloys containing at least 200 parts per million oxygenwhich comprises:

a. preparing a bath of molten copper-nickel alloy,

b. taking samples of said molten copper-nickel alloy at time intervalswhile adding nickel to said molten copper-nickel alloy,

c. measuring the electromotive force across a galvanic cell insertedinto said molten copper-nickel alloy simultaneously with the taking ofeach sample, wherein one electrode comprises said molten copper-nickelalloy, the other electrode is a reference electrode comprising a mixtureofa metal and its oxide or a gas of known oxygen potential at the sametemperature as said molten copper-nickel alloy and the electrolyte is asolid anionic conductor,

d. analyzing each sample for nickel,

e. plotting calibration curves of nickel versus electromotive forcebased on electromotive force measurements from step (e) and nickelanalyses from step (d), and I f. in a second bath of moltencopper-nickel alloy containing at least 200 parts per million oxygen,measuring in said second bath the electromotive force as in step (c) andobtaining from the calibration curve plotted in step (e) theconcentration of nickel in said second bath of molten copper-nickelbronze simultaneously with the taking of each sample,'wherein oneelectrode comprises said molten aluminum-bronze, the other electrode isa reference electrode comprising a mixture of a metal and its oxide or agas of known oxygen potential at the same temperature as said moltenaluminum-bronze t and the electrolyte is a solid anionic conductor, (1.analyzing each sample for aluminum,

e. plotting calibration curves of aluminum versus electromotive forcebased on electromotive force measurements from step (c) and aluminumanalyses from step (d), and

in a second bath of molten aluminum-bronze containing at least 1.0 partsper million oxygen, measuringin said second bath the electromotive forceas in step (c) and obtaining from the calibration curve plotted in step(e) the concentration of aluminum in said second bath of moltenaluminumbronze.

4. A method of determining the concentration of chromium in moltenstainless steel containing at least 1.0 parts per million oxygen whichcomprises:

a. preparing a bath of molten stainless steel,

b. taking samples of said molten stainless steel at time intervals whileadding chromium to said molten stainless steel,

c. measuring the electromotive force across a galvanic cell insertedinto said molten stainless steel simultaneously with the taking of eachsample, wherein one electrode comprises said molten stainless steel, theother electrode is a reference electrodercomprising a mixture of a metaland its oxide or a gas of known oxygen potential at the same temperatureas said molten stainless steel and the electrolyte is a solid anionicconductor,

d. analyzing each sample for chromium,

e. plotting calibration curves of chromium versus electromotive forcebased on electromotive force measurements from step (c) and chromiumanalyses from step (d), and

f. in a second bath of molten stainless steel containing at least 1.0parts per million oxygen, measuring in said second vbath theelectromotive force as step (c) and obtaining from the calibration curveplotted in step (e) the concentration of chromium in said second bath ofmolten stainless steel.

5. A method of measuring the concentration of a metal in a melt of analloy, said metal having an oxide which has an oxygen potential lessthan that of the oxygen normally dissolved in the solvent metal of amolten alloy, said molten alloy selected from thegroup consisting ofcopper-nickel alloys, aluminum-bronzes, brasses and stainless steels,wherein said metal having an oxide which has an oxygen potential lessthan that of the oxygen normally dissolved in the solvent metal isnickel in molten copper-nickel alloys, aluminum in moltenaluminum-bronzes, zinc in molten brasses, and chromium in moltenstainless steels, which method comprises:

a. preparing a bath of a molten alloy selected from the group consistingof copper-nickel alloys containing at least 200 parts per millionoxygen, aluminum-bronzes containing at least 1 part per million oxygen,brasses containing at least 0.005 parts per million oxygen','andstainless steels containing at least 1 part per million oxygen,

b.taking samples of said molten alloy at time intervals while addingnickel to said copper-nickel alloys, aluminum to said aluminum-bronzes,zinc to said brasses and chromium to said stainless steels,

c. measuring the electromotive force across a galvanic cell insertedinto said molten. alloy simultaneously with the taking of each sample,wherein one electrode comprises said molten alloy, the other electrodeis a reference electrode comprising a mixture ofa metal and its oxide ora gas of known oxygen potential at the same temperature as said moltenalloy and the electrolyte is a solid anionic conductor,

d. analyzing each sample for nickel in said coppernickel alloys,aluminum in said aluminum-bronzes, Zinc in said brasses and chromium insaid stainless steels,

e. plotting calibration curves of nickel versus electromotive force,aluminum versus electromotive force, zinc versus electromotive force,and chromium versus electromotive force based on electromotive forcemeasurements from step (c) and nickel, aluminum, zinc and chromiumanalyses from step (d), and

f. in a second bath of a molten alloy selected from the group consistingof copper-nickel alloys containing at least 200 parts per millionoxygen, aluminumbronzes containing at least 1 part per million oxygen,brasses containing at least 0.005 parts per million oxygen and stainlesssteels containing at least 1 part per million oxygen, measuring in saidsecond baththe electromotive force as in step (c) and obtain from theappropriate calibration curve plotted in step (e) the concentration ofnickel in said second bath of molten copper-nickel alloy, aluminum insaid second bath of molten aluminum-bronze, zinc in said second bath ofmolten'brass and chromium in said second bath of molten stainless steel.

2. A method of determining the concentration of nickel in moltencopper-nickel alloys containing at least 200 parts per million oxygenwhich comprises: a. preparing a bath of molten copper-nickel alloy, b.taking samples of said molten copper-nickel alloy at time intervalswhile adding nickel to said molten copper-nickel alloy, c. measuring theelectromotive force across a galvanic cell inserted into said moltencopper-nickel alloy simultaneously with the taking of each sample,wherein one electrode comprises said molten copper-nickel alloy, theother electrode is a reference electrode comprising a mixture of a metaland its oxide or a gas of known oxygen potential at the same temperatureas said molten copper-nickel alloy and the electrolyte is a solidanionic conductor, d. analyzing each sample for nickel, e. plottingcalibration curves of nickel versus electromotive force based onelectromotive force measurements from step (c) and nickel analyses fromstep (d), and f. in a second bath of molten copper-nickel alloycontaining at least 200 parts per million oxygen, measuring in saidsecond bath the electromotive force as in step (c) and obtaining fromthe calibration curve plotted in step (e) the concentration of nickel insaid second bath of molten copper-nickel alloy.
 3. A method ofdetermining the concentration of aluminum in molten aluminum-bronzescontaining at least 1.0 parts per million oxygen which comprises: a.preparing a bath of molten aluminum-bronze, b. taking samples of saidmolten aluminum-bronze at time intervals while adding aluminum to saidmolten aluminum bronze alloy, c. measuring the electromotive forceacross a galvanic cell inserted into said molten aluminum-bronzesimultaneously with the taking of each sample, wherein one electrodecomprises said molten aluminum-bronze, the other electrode is areference electrode comprising a mixture of a metal and its oxide or agas of known oxygen potential at the same temperature as said moltenaluminum-bronze and the electrolyte is a solid anionic conductor, d.analyzing each sample for aluminum, e. plotting calibration curves ofaluminum versus electromotive force based on electromotive forcemeasurements from step (c) and aluminum analyses from step (d), and f.in a second bath of molten aluminum-bronze containing at least 1.0 partsper million oxygen, measuring in said second bath the electromotiveforce as in step (c) and obtaining from the calibration curve plotted instep (e) the concentration of aluminum in said second bath of moltenaluminum-bronze.
 4. A method of determining the concentration ofchromium in molten stainless steel containing at least 1.0 parts permillion oxygen which comprises: a. preparing a bath of molten stainlesssteel, b. taking samples of said molten stainless steel at timeintervals while adding chromium to said molten stainless steel, c.measuring the electromotive force across a galvanic cell inserted intosaid molten stainless steel simultaneously with the taking of eachsample, wherein one electrode comprises said molten stainless steel, theother electrode is a reference electrode comprising a mixture of a metaland its oxide or a gas of known oxygen potential at the same temperatureas said molten stainless steel and the electrolyte is a solid anionicconductor, d. analyzing each sample for chromium, e. plottingcalibration curves of chromium versus electromotive force based onelectromotive force measurements from step (c) and chromium analysesfrom step (d), and f. in a second bath of molten stainless steelcontaining at least 1.0 parts per million oxygen, measuring in saidsecond bath the electromotive force as step (c) and obtaining from thecalibration curve plotted in step (e) the concentration of chromium insaid second bath of molten stainless steel.
 5. A method of measuring theconcentration of a metal in a melt of an alloy, said metal having anoxide which has an oxygen potential less than that of the oxygennormally dissolved in the solvent metal of a molten alloy, said moltenalloy selected from the group consisting of copper-nickel alloys,aluminum-bronzes, brasses and stainless steels, wherein said metalhaving an oxide which has an oxygen potential less than that of theoxygen normally dissolved in the solvent metal is nickel in moltencopper-nickel alloys, aluminum in molten aluminum-bronzes, zinc inmolten brasses, and chromium in molten stainless steels, which methodcomprises: a. preparing a bath of a molten alloy selected from the groupconsisting of copper-nickel alloys containing at least 200 parts permillion oxygen, aluminum-bronzes containing at least 1 part per millionoxygen, brasses containing at least 0.005 parts per million oxygen, andstainless steels containing at least 1 part per million oxygen, b.taking samples of said molten alloy at time intervals while addingnickel to said copper-nickel alloys, aluminum to said aluminum-bronzes,zinc to said brasses and chromium to said stainless steels, c. measuringthe electromotive force across a galvanic cell inserted into said moltenalloy simultaneously with the taking of each sample, wherein oneelectrode comprises said molten alloy, the other electrode is areference electrode comprising a mixture of a metal and its oxide or agas of known oxygen potential at the same temperature as said moltenalloy and the electrolyte is a solid anionic conductor, d. analyzingeach sample for nickel in said copper-nickel alloys, aluminum in saidaluminum-bronzes, zinc in said brasses and chromium in said stainlesssteels, e. plotting calibration curves of nickel versus electromotiveforce, aluminum versus electromotive force, zinc versus electromotiveforce, and chromium versus electromotive force based on electromotiveforce measurements from step (c) and nickel, aluminum, zinc and chromiumanalyses from step (d), and f. in a second bath of a molten alloyselected from the group consisting of copper-nickel alloys containing atleast 200 parts per million oxygen, aluminum-bronzes containing at least1 part per million oxygen, brasses containing at least 0.005 parts permillion oxygen and stainless steels containing at least 1 part permillion oxygen, measuring in said second bath the electromotive force asin step (c) and obtain from the appropriate calibration curve plotted instep (e) the concentration of nickel in said second bath of moltencopper-nickel alloy, aluminum in said second bath of moltenaluminum-bronze, zinc in said second bath of molten brass and chromiumin said second bath of molten stainless steel.